The present invention relates to a flow-through cell provided with a reference electrode. Particularly, the invention relates to a flow-through cell suitable for measuring ions contained in a blood sample.
A combination of an ion-selective electrode and a reference electrode can be employed for measuring ions such as sodium, potassium, chloride ions, etc. contained in a blood sample. A flow-through cell, which has an open flow path, is so designed that a reference electrode solution flows into a path for a sample solution. In such a flow-through cell, a disturbance of the interface between the reference electrode solution and the sample solution often gives an adverse influence on the measurement of the ion concentration.
In H. F. Osswald et al, Chimia, 31 (1977), No. 2, there is disclosed a flow-through electrode, wherein a sample is flowed down through a vertical path and a reference electrode solution is flowed through a path which is narrower than the vertical sample path and then the reference electrode solution is delivered from an obliquely lower position to a middle part of the vertical sample path in order to suppress the disturbance of the interface between these two streams. However, this prior art has such a drawback that, since the electrode solution is passed through a narrow path, a number of bubbles stagnate on a connector member disposed between the solution reservoir and the narrow path, and a portion of the bubbles flow through the narrow path to the interface between the two streams. In addition, the narrow path is sometimes clogged with a particulate contaminant contained in the reference electrode solution. Therefore, the flow-through system according to Osswald et al. lacks a long term stability.
According to the prior art disclosed in Japanese Utility Model Patent Application (Laid-Open) No. 29759/1984, a valve is disposed in a path between a reference electrode and an ion-selective electrode, in order to suppress a disturbance of the interface between the two streams in question. However, in this prior art, the difference in specific gravity between the blood sample and the reference electrode solution may bring about an adverse effect on the interface stability.
Japanese Patent Application (Laid-Open) No. 169,756/1986 discloses a flow-through cell, wherein a sample path having a shape of circular loop is provided in the flow cell and a path for the reference electrode solution is connected to a middle portion of the loop path for the purpose of obtaining a stabilized potential between the two solutions. In this prior art, it is difficult to remove bubbles from the paths.